Spinal rods are often used in the surgical treatment of spinal disorders such as degenerative disc disease, disc herniations, scoliosis or other curvature abnormalities, and fractures. Different types of surgical treatments are used. In some cases, spinal fusion is indicated to inhibit relative motion between vertebral bodies. In other cases, dynamic implants are used to preserve motion between vertebral bodies. For either type of surgical treatment, spinal rods may be attached to the exterior of two or more vertebrae, whether it is at a posterior, anterior, or lateral side of the vertebrae. In other embodiments, spinal rods are attached to the vertebrae without the use of dynamic implants or spinal fusion.
Spinal rods may provide a stable, rigid column that encourages bones to fuse after spinal-fusion surgery. Further, the rods may redirect stresses over a wider area away from a damaged or defective region. Also, a rigid rod may restore the spine to its proper alignment. In some cases, a flexible rod may be appropriate. Flexible rods may provide some advantages over rigid rods, such as increasing loading on interbody constructs, decreasing stress transfer to adjacent vertebral elements while bone-graft healing takes place, and generally balancing strength with flexibility.
It is sometimes the case, such as with degenerative diseases, that vertebral levels adjacent to a previously implanted spinal rod may begin to deteriorate. In other cases, such as with spinal correction, a surgeon may elect to insert spinal rods in stages. In either case, revision surgeries may be indicated to secure additional vertebral levels with longer spinal rods. These types of surgeries usually require detachment and removal of the originally implanted rods and insertion of a longer rod into the existing anchors. However, a surgeon may prefer to leave the original implant intact to preserve fusion sites and/or implant geometry. Accordingly, conventional spinal rod systems may not permit extendable attachment of additional spinal rods to previously implanted spinal rods.